Should I opt for an MRI for a 10 month old child banged her head on a chair?

Hello doctor,

I have a 16-month-old child. When she was 10 months old, she banged her head between her eyes, inner left brow rather firmly on a blunt object. She was attempting to stand up holding onto a chair, and when she quickly sat, her head firmly bumped the bottom of the portion of the chair which is made of metal. She cried immediately and vomited once but otherwise seemed fine and in a short time was back to play. From all, I read online, and the other family around there was no need to go to emergency. A few weeks later, I started to notice subtle changes. She developed a deep scowl that seemed to favor her left side where she hit. Also, the mark where she hit still came out when she was upset (it still does) and rubbing ensued. I took her into her Pediatrician and told him all three weeks after it happened. I Showed him pictures of the chair where she hit as well as images of her the day after and tried to explain the scowl, the rubbing, and just how I felt something was amiss. He assured me she had none of the symptoms associated with severe head trauma. Six months later and a few visits then all for the same thing I am still unsure and wish we could have look to make sure no tissue or other damage has been done. My question is, if internal damage was done to a vessel or two or a small fracture occurred, is it possible for the symptoms to be slight at this time and if there is a minor ever so slight bleed inside, could it take months if not years for visible signs to occur and irreversible damage to follow suit? Would it not then be too late? Should I push for cranial sonography or magnetic resonance imaging (MRI)?